HDFS-11998. Enable DFSNetworkTopology as default. Contributed by Chen Liang.

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/DFSConfigKeys.java

@@ -987,7 +987,7 @@ public class DFSConfigKeys extends CommonConfigurationKeys {
 
   public static final String DFS_USE_DFS_NETWORK_TOPOLOGY_KEY =
       "dfs.use.dfs.network.topology";
-  public static final boolean DFS_USE_DFS_NETWORK_TOPOLOGY_DEFAULT = false;
+  public static final boolean DFS_USE_DFS_NETWORK_TOPOLOGY_DEFAULT = true;
 
   // dfs.client.retry confs are moved to HdfsClientConfigKeys.Retry 
   @Deprecated

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/AvailableSpaceBlockPlacementPolicy.java

@@ -24,10 +24,13 @@ import static org.apache.hadoop.hdfs.DFSConfigKeys.DFS_NAMENODE_AVAILABLE_SPACE_
 import java.util.Collection;
 import java.util.Random;
 
+import com.google.common.base.Preconditions;
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
 import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.fs.StorageType;
 import org.apache.hadoop.hdfs.DFSConfigKeys;
+import org.apache.hadoop.hdfs.net.DFSNetworkTopology;
 import org.apache.hadoop.net.NetworkTopology;
 import org.apache.hadoop.net.Node;
 
@@ -69,6 +72,19 @@ public class AvailableSpaceBlockPlacementPolicy extends
     balancedPreference = (int) (100 * balancedPreferencePercent);
   }
 
+  @Override
+  protected DatanodeDescriptor chooseDataNode(final String scope,
+      final Collection<Node> excludedNode, StorageType type) {
+    // only the code that uses DFSNetworkTopology should trigger this code path.
+    Preconditions.checkArgument(clusterMap instanceof DFSNetworkTopology);
+    DFSNetworkTopology dfsClusterMap = (DFSNetworkTopology)clusterMap;
+    DatanodeDescriptor a = (DatanodeDescriptor) dfsClusterMap
+        .chooseRandomWithStorageType(scope, excludedNode, type);
+    DatanodeDescriptor b = (DatanodeDescriptor) dfsClusterMap
+        .chooseRandomWithStorageType(scope, excludedNode, type);
+    return select(a, b);
+  }
+
   @Override
   protected DatanodeDescriptor chooseDataNode(final String scope,
       final Collection<Node> excludedNode) {
@@ -76,6 +92,11 @@ public class AvailableSpaceBlockPlacementPolicy extends
         (DatanodeDescriptor) clusterMap.chooseRandom(scope, excludedNode);
     DatanodeDescriptor b =
         (DatanodeDescriptor) clusterMap.chooseRandom(scope, excludedNode);
+    return select(a, b);
+  }
+
+  private DatanodeDescriptor select(
+      DatanodeDescriptor a, DatanodeDescriptor b) {
     if (a != null && b != null){
       int ret = compareDataNode(a, b);
       if (ret == 0) {

hadoop-hdfs-project/hadoop-hdfs/src/main/resources/hdfs-default.xml

@@ -4286,7 +4286,7 @@
 
   <property>
     <name>dfs.use.dfs.network.topology</name>
-    <value>false</value>
+    <value>true</value>
     <description>
      Enables DFSNetworkTopology to choose nodes for placing replicas.
     </description>

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/blockmanagement/TestReplicationPolicyWithNodeGroup.java

@@ -17,6 +17,7 @@
  */
 package org.apache.hadoop.hdfs.server.blockmanagement;
 
+import static org.apache.hadoop.hdfs.DFSConfigKeys.DFS_USE_DFS_NETWORK_TOPOLOGY_KEY;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertTrue;
@@ -51,6 +52,9 @@ public class TestReplicationPolicyWithNodeGroup extends BaseReplicationPolicyTes
 
   @Override
   DatanodeDescriptor[] getDatanodeDescriptors(Configuration conf) {
+    // default is true, in this case this test will against DFSNetworkTopology
+    // but it run on NetworkTopologyWithNodeGroup, so set to false.
+    conf.setBoolean(DFS_USE_DFS_NETWORK_TOPOLOGY_KEY, false);
     conf.set(CommonConfigurationKeysPublic.NET_TOPOLOGY_IMPL_KEY,
             NetworkTopologyWithNodeGroup.class.getName());
     final String[] racks = {